Glaucoma is an eye condition in which the hydrostatic pressure within the eye is abnormally high, thereby resulting in damage to the optic nerve. There are many treatments for the glaucoma condition that involve lowering the intraocular pressure, either by means of medication or surgery.
Medicinal treatments either decrease the rate at which aqueous humor is pumped into the eye or improve the outflow of aqueous humor from the eye.
There are three primary surgical methods for treating glaucoma. Presently, none of them are a complete answer to the problem:
a) Cyclodestructive procedures damage the ciliary body of the eye and decrease the rate of aqueous humor production. The main problem is the extremely fine dividing line between too little and too much treatment. This treatment often does not work, or it works too well. When the surgery works too well, a hypotonous eye may develop in which the pressure is too low for normal ocular function and health.
b) Laser therapy of the trabecular meshwork is used to decrease the resistance of outflow of aqueous humor into the Canal of Schlemm. The main problem with this procedure is that it only provides relief for about five years. Re-treatment is often unsuccessful because it may cause too much scarring of the outflow channels. Thus, this procedure can do more harm than good.
c) Shunting of aqueous humor from the anterior chamber through the sclera to outside of the confines of the eye is the most common surgical procedure. Among the shunting procedures, the often-performed trabeculectomy is a type of filtering method. It allows aqueous humor to “filter” out of the eye. A channel is created from the anterior chamber under a scleral flap to the episcleral space. The main problem with this procedure is that the outcome depends on the individual healing properties of the eye in the post-operative period. Trabeculectomy is often much less successful in highly pigmented eyes and eyes with previous surgery, rubeosis, or chronic uveitis. To overcome this problem, several shunts have been devised to carry aqueous humor from the anterior chamber to the episcleral space. Scarring often occurs surrounding the exterior end when shunts are used. This renders the outcome unpredictable.
Another problem with these types of surgical procedures is that the globe is left with a transcleral fistula. The fistula renders the eye susceptible to the ingress of organisms and intraocular infection. This condition is known as endophthalmitis and can be devastating to the eye, since the eye is not naturally designed to defend against this type of onslaught.
The invention seeks to provide a surgical treatment and apparatus that will overcome the many problems associated with present-day surgical procedures.
The current invention provides an indwelling shunt that diverts aqueous humor from the anterior chamber to the blood flowing in the choroidal and uveal tissues. This decreases the intraocular pressure of the glaucomatous eye. The indwelling shunt maintains the area of exposure of aqueous humor with the uvea by physically preventing scarring of the surrounding tissues. The method utilizes the normally occurring 25 mm Hg driving force of the protein colloid osmotic pressure of the blood to maximize the flow of aqueous humor out of the eye (Yablonski, M. E., J of Glaucoma, February 2003, 12(1):90-92).
One of the many problems that this inventive procedure overcomes is the normally low outflow of aqueous humor into the uveal blood caused by the normally low hydraulic permeability between the aqueous humor of the anterior chamber and the uveal blood vessels (Yablonski, ibid.). The internal tube shunt of this invention, however, greatly increases the hydraulic permeability between the aqueous humor and the uveal blood vessels, thus greatly increasing the magnitude of the outflow via this route.
The present invention overcomes the two main objections of most of the current surgical approaches: (a) it requires no permanent transcleral route for the egress of aqueous humor from the eye, and (b) the success of the procedure is not as dependent on the individual healing properties of the eye as it is in other procedures. Therefore, the inventive technique not only works in younger eyes, but it also works in eyes of darkly pigmented individuals, and eyes of patients who have had previous surgery. In addition, the inventive procedure leaves no transcleral route in the eye, thus decreasing the susceptibility to endophthalmitis.
In an article by Stegmann (1990), a procedure is described wherein a non-penetrating deep sclerectomy is performed. The procedure was called “viscocanalostomy” because a viscoelastic substance was injected into the cut ends of the canal of Schlemm after the canal was exposed. Like the present technique, Stegmann first created a thin scleral flap, then created a deep sclerectomy by removing the deep sclera, leaving only a thin layer of sclera of 50 to 100 microns in thickness overlying the choroidal tissue beneath.
It should be observed that Stegmann sutured the overlying scleral flap very tightly, thereby eliminating a final transcleral route for aqueous humor drainage. This implied that the intended mechanism for aqueous humor egress was an intraocular shunt. The mechanism of action of the procedure was proposed by Stegmann to be the access of aqueous humor to the newly dilated canal of Schlemm, from which it flowed from the eye by the usual outflow routes. However, if this were the case, the outflow facility of the eyes should be increased, as measured by tonography. No studies have shown an increase in outflow facility after the viscocanalostomy is performed, despite a marked decrease in intraocular pressure.
Another related technique to that of the current invention is the procedure that sutures a collagen implant beneath the scleral flap into the bed of the deep sclerectomy (M. E. Karlen, E. Sanchez, C. C. Schnyder, M. Sickenberg, and A. Mermoud, Deep sclerectomy with collagen implant: medium term results, Br J Ophthalmol, January 1999, 83(1):6-11). The method provides a non-penetrating deep sclerectomy wherein a collagen implant is placed between the overlying scleral flap and the underlying suprachoroidal space. No dilation of the canal of Schlemm is performed. No flow of aqueous humor into the uveal blood is suggested, and only two scleral flap sutures are used, which renders the scleral flap permeable to transcleral flow and creates a transcleral fistula.
In U.S. Pat. No. 6,383,219, issued on May 7, 2002 to Telandro et al., a related non-penetrating deep sclerectomy is illustrated. The method uses an implant made of a cross-linked hydraluronic acid material, which is shaped like a polyhedron having at least five faces. The material is placed between the overlying scleral flap and the underlying suprachoroidal scleral bed. Unlike the current inventive method, this procedure does not propose that the aqueous humor flows mainly into the adjacent uveal blood in response to its protein colloid osmotic pressure. The use of only two sutures in the overlying scleral flap renders this flap permeable to transcleral flow, creating a transcleral fistula.
The stated mechanism for relief in Telandro et al. is the high water content that acts like a wick, i.e., it transports the ocular fluids by capillary action. No mention is made of flow of aqueous humor into the uveal blood, and it is implied that the final destination of the flow of aqueous humor is across the overlying scleral flap into the episcleral space. This method is similar to a conventional trabeculectomy and other filtering procedures.
Some internal shunts have previously been proposed. In U.S. Pat. No. 6,450,984, issued to Lynch and Brown on Sep. 17, 2002, a shunt is illustrated that shunts fluid from the anterior chamber. The shunt is placed under a scleral flap and into the open ends of the canal of Schlemm. This method requires normal drainage of aqueous humor from the canal of Schlemm into the episcleral veins. Since in open angle glaucoma, which is the most common type of glaucoma, flow through the canal of Schlemm is impaired, this technique appears flawed. To the best of knowledge and belief, no reports exist in the literature depicting the successful implementation of this technique.
In U.S. Pat. No. 5,601,094, issued on Feb. 11, 1997 to Reiss, a shunt is described which causes flow of aqueous humor from the anterior chamber to the suprachoroidal space. Unlike the present invention, however, the shunt is exteriorized before it enters the suprachoroidal space. This renders the eye susceptible to endopthalmitis. To the best of knowledge and belief, there have been no successful reports for this technique in the literature.
In U.S. Pat. No. 4,521,210, issued on Jun. 4, 1985 to Wong, a shunt is illustrated that extends from the anterior chamber to the suprachoroidal space. The shunt is designed to create a permanent cyclodialysis cleft and shunt aqueous fluid to the suprachoroidal space from the anterior chamber. The suprachoroidal space is surgically entered and the ciliary body disinserted from the scleral spur. To the best of knowledge and belief, there have not been any reports in the literature of the success of this technique.